Cocks or taps as used in hospitals, domestic homes for use over sinks, tubs and basins are usually operated by a screw or lever action where the valve sealing member is applied by manual pressure onto the valve seat.
While this effectively closes and prevents the flow of water, there is often a tendency to apply too much force and this excessive pressure damages the sealing washer so that in order to prevent leakage further pressure is often applied.
Also in hospitals and like institutions, lever operation is often essential, where the tap is operated by an elbow, arm or knee and also due to the length of the lever excessive pressure can be applied during the closing operation.
Additionally in some installations, such as in public conveniences, hotels, motels and the like, the cocks should be such that they are less prone to vandalism where often portions of the tap or cock such as knobs, handles and the like are often removed.